    Patent document 1: JP H08-159733 A    Patent document 2: JP H09-021611 A (U.S. Pat. No. 5,801,763)    Patent document 3: JP 2005-301742 A (US 2005/0226472)    Patent document 4: JP 2005-354155 A (US 2005/0270413)    Patent document 5: JP 2010-176382 A
According to a disclosed driver state detection apparatus, a camera provided in a vehicle compartment captures a driver's face. The apparatus processes the captured face image and extracts facial feature points such as an eye, nose, and mouth. Based on feature point positions or an opened or closed state of the eyes, the apparatus detects driving states such as the driver's facial orientation and drowsy driving. The driver state detection apparatus uses an infrared strobe light or LED to illuminate and capture the driver's face. The infrared strobe light or LED has a near-infrared wavelength and is provided near the camera.
Positions of a retina reflection image and a cornea reflection image in an eyeball can be acquired as image information to measure reflection images from the vehicle driver's eyeball. The pupil contracts under intense outside light such as the sunlight and decreases the light intensity that reaches the retina through the pupil. This makes it difficult to acquire a reflection image from the retina and degrades the measurement accuracy in an eye direction. The vehicular eye direction measurement apparatus disclosed in patent document 1 decreases a noise due to the outside light by accelerating the shutter speed and increasing the peak power of illumination light. The apparatus can accurately extract a reflection image without increasing the measurement time.
According to the face image capturing apparatus disclosed in patent document 2, the eye detection means detects a test subject's eye based on the test subject's face image captured by the two-dimensional capturing means. If the eye detection means does not detect the test subject's eye, the infrared illuminating means is activated to capture the driver's face image. Even if the driver wears his or her glasses, the infrared illuminating means can minimize an effect of the light reflected in the lens surface of glasses. The infrared illuminating means illuminates at least the test subject's face with infrared light passing through an optical filter. The infrared illuminating means is provided so that the optical axis of the two-dimensional capturing means and the optical axis of the infrared light form an angle larger than or equal to the predetermined angle.
The driver appearance recognition system disclosed in patent document 3 can extend service life of the infrared illuminating means. For this purpose, various appearance recognition processes change the illuminance of a face image captured by the camera to necessary illuminance.
The motion picture capturing apparatus disclosed in patent document 4 can adaptively adjust the amount of luminescence of a lighting apparatus under a low-illuminance environment in accordance with changes in the brightness of an object.
The lighting apparatus disclosed in patent document 5 frees a driver from a feeling of strangeness. The vehicle may operate its illumination portion and stops its engine. In this case, the lighting apparatus adjusts the irradiating light intensity mainly based on the environment light illumination detected by the environment light detection portion. The vehicle may operate its illumination portion and its engine. In this case, the lighting apparatus adjusts the irradiating light intensity mainly based on a recognition result notified from the recognition portion.
As described in patent document 1, for example, feature points on the driver's face may be detected under such intense outside light as to reflect the surrounding landscape in driver's glasses. In such a case, the illumination is preferably more intense than the sunlight. For example, the light source such as an LED may be activated in pulses synchronously with the image capturing timing. This can radiate the light more intensely than steady lighting. In terms of the LED light source wavelength, the invisible near-infrared light is generally used in order to protect the driver against unpleasant feeling or prevent driving troubles in the night. It is practical to select a low-wavelength LED from the near-infrared light in order to ensure the sensitivity of an image capturing system. Generally, such an LED contains visible components that may be perceived to be red depending on the driver's visual feature. The driver may feel a perceptible flicker especially in the night or darkness depending on the image capturing timing.
Steadily activating the illumination can prevent a flicker. However, the rated LED current magnitude generates weak emission intensity and is too small to prevent the glasses from reflecting the landscape. For example, many LEDs may be provided in array to ensure the sufficient emission intensity. However, this increases costs.
The technologies disclosed in patent documents 2 through 5 adjust the emission intensity (light intensity) of the irradiating light (LED) in accordance with the detected eye state, the occupant appearance recognition process, the object brightness, or operational situations of the illumination portion and the engine. However, patent documents 2 through 5 do not disclose or suggest considerations on the visual sense such as flicker prevention or emission intensity adjustment.